Origin of Israel as a Nation
On Jacob's way back to the land of his fathers as the Lord commanded him, Jacob wrestled with a man and prevailed. This man later changed the name of Jacob to Israel and gave him blessings. All Jacob's descendants came to be known as Israelites since that time. (Genesis 32:24-29)
12 Tribes of Israel
Israel's 12 sons then became the 12 Tribes of Israel. The names of these twelve Tribes according to the age of their fathers (from eldest to youngest) are listed as follows:
14 Tribes of Israel
Before Jacob passed away, he established the two sons of his son Joseph, Ephraim and Manasseh as his own sons so they can receive blessings directly from him. Two more tribes were therefore added to Israel to become fourteen tribes. Furthermore, Jacob gave Joseph's younger son Ephraim greater blessings than his elder son Manasseh. (Genesis 48:18-19)
13. Ephraim (younger son of Joseph)
14. Manasseh (elder son of Joseph)
And now your (Joseph's) two sons, Ephraim and Manasseh, which were born unto you in the land of Egypt before I (Jacob) came unto you into Egypt, are mine; as Reuben and Simeon, they shall be mine. Genesis 48:5
14 Tribes became 12 Tribes Again
In the Book of Revelation, when angels put a mark on the children of Israel, only twelve Tribes were counted. Dan and Ephraim were not on the list!
And there came to my ears the number of those who had the mark on their brows, a hundred and forty-four thousand, who were marked out of every tribe of the people of Israel. Of the tribe of Judah were sealed twelve thousand ..... Judah ..... Reuben ..... Gad ..... Asher ..... Naphtali ..... Manasseh ..... Simeon ..... Levi ..... Issachar ..... Zebulun ..... Joseph ..... Benjamin. Revelation 7:4-8
This was again confirmed in Revelations where New Jerusalem was described to have twelve doors only, and not fourteen! On each of these twelve doors, the names of the twelve Tribes of the children of Israel were written.
She (New Jerusalem) had a wall great and high, with twelve doors, and at the doors twelve angels; and names on them, which are the names of the twelve tribes of the children of Israel. Revelation 21:12
Why Was Ephraim and Dan Cut Off from Israel?
The Bible did not answer this question directly. However, since both Ephraim and Dan were removed from the tribes of Israel, they must have both done something sinful enough to cut themselves off from their inheritance and their father Jacob's blessings. The event most likely to have caused their removal was when the first king of the northern Kingdom of Israel, Jeroboam from the tribe of Ephraim built two calves of gold for their people to worship. He then set one in Bethel in the land of Ephraim, and the other he set in Dan.
After seeking advice, the king made two golden calves. He said to the people, “It is too much for you to go up to Jerusalem. Here are your gods, Israel, who brought you up out of Egypt.” One he set one up in Bethel, and the other in Dan. And this thing became a sin; the people came to worship the one at Bethel and went as far as Dan to worship the other. 1 Kings 12:28-30
King Jeroboam did this to prevent the children of the northern Kingdom to return to Jerusalem to worship, whereby they may re-unite with the southern Kingdom and turn against him. However, in doing so, he led the children of Israel to turn away from Yahweh to worship idols, and have defiled the lands of Ephraim and Dan.
Warning to Us
This incident is a reminder to us that, even after we have obtained blessings (salvation) from God, it is possible for us to lose it if we are not cautious enough to keep all His commandments. Even though our Lord is merciful, He is also a just ruler, and we must stay away from any kind of idol worships.